This invention relates to position-to-signal converting technology and, more particularly, to a position transducer system with a built-in calibrator for moving objects, a method for exactly determining the position of a moving object and a keyboard musical instrument equipped with the position transducer system.
While a pianist is playing a piano, he or she selectively depresses the black/white keys and, thereafter, releases them so as to generate acoustic tones. The depressed black/white key actuates the associated damper mechanism and the associated key action mechanism. The depressed black/white key lifts the damper felt, and the damper felt is spaced from the associated set of strings so as to allow the set of strings to vibrate. On the other hand, the key action mechanism drives the associated hammer to rotate, and the hammer felt strikes the set of strings. Then the strings vibrate to generate the acoustic tone. When the pianist releases the depressed black/white key, the black/white key returns toward the rest position. The released black/white key brings the damper felt into contact with the set of strings, again, and damps the vibrations of the set of strings. This extinguishes the acoustic tone. If the pianist depresses pedals, i.e., a damper pedal, a sustaining pedal and a soft pedal, the pedal mechanisms impart predetermined effects to the acoustic tones. Thus, the acoustic piano repeats the loop having depressing a black/white key, striking the strings, releasing the black/white key and damping the vibrations during the performance, and the pedals selectively impart the expressions to the acoustic tones.
An automatic player piano is an acoustic piano equipped with a recording system and a playback system. While a pianist is playing the acoustic piano, each of the black/white keys generates the acoustic tone through the above-described steps, and the pedal mechanisms selectively impart the expressions to the acoustic tones. The recording system monitors the black/white keys so as to generate pieces of music data information representative of the performance. The pieces of music data information are stored in a suitable information storage medium. Otherwise, a tone generator and a sound system produce electronic sounds on the basis of the pieces of music data information in a real time fashion. When the pianist instructs the automatic player piano to reproduce the performance, the playback system reads out the pieces of music data information from the information storage medium, and the actuators selectively actuate the black/white keys and the pedals.
An automatic player piano may be equipped with a silent system. The silent system includes a hammer stopper, which is usually provided between the hammer shanks and the sets of strings. The hammer stopper is adjustable between a free position and a blocking position. While a pianist is playing a tune on the keyboard, the black/white keys are selectively depressed, and the hammer assemblies escape from the associated jacks. Then, the hammer assembly associated with a depressed key starts to rotate freely. The hammer stopper in the free position allows the hammer to strike the set of stings, and the strings vibrate to generate an acoustic tone. However, if the hammer stopper is in the blocking position, the hammer assembly rebounds on the hammer stopper before striking the strings, and no acoustic tone is generated. A key sensor monitors the associated black/white key, and reports the key motion to a tone generator. The tone generator produces a tone signal, and an electronic sound is reproduced through a headphone.
An automatic player piano may be equipped with a silent system. The silent system includes a hammer stopper, which is usually provided between the hammer shanks and the sets of strings. The hammer stopper is changed between a free position and a blocking position. While a pianist is playing a tune on the keyboard, the black/white keys are selectively depressed, and the hammer assemblies escape from the associated jacks. Then, the hammer assembly associated with a depressed key starts a free rotation. The hammer stopper in the free position allows the hammer to strike the set of strings, and the strings vibrate for generating an acoustic tone. However, if the hammer stopper is in the blocking position, the hammer assembly rebounds on the hammer stopper before striking the strings, and any acoustic tone is not generated. A key sensor monitors the associated black/white key, and reports the key motion to a tone generator. The tone generator produces a tone signal, and an electronic sound is reproduced through a headphone.
A shutter plate attached to the associated key and a photo sensor mounted on the key bed form in combination a typical example of the key sensor. However, the prior art key sensor merely detects a couple of points on the trajectory of the associated key, and a data processor calculates the key velocity on the basis of the distance between the detecting points and a lapse of time therebetween.
Another prior art key sensor available for an automatic player piano is disclosed in Japanese Patent Publication of Unexamined Application (laid-open) No. 9-54584. The prior art key sensor continuously detects the key moving on a trajectory.
An opto-electronic sensing device is disclosed in U.S. Pat. No. 5,001,339, assigned to Gulbransen Incorporated. The opto-electronic sensing device is also available for detecting a key motion of an acoustic piano. The opto-electronic sensing device has a flag held in contact with the lower surface of the key at all times, and an opto-electronic sensor monitors the flag so as to generate an output signal indicative of the current position of the flag and, accordingly, the key.
The prior art key sensor disclosed in the Japanese Patent Publication of Unexamined Application needs to eliminate noise components due to individualities of the key sensor and a fitting error from the output signal. For this reason, calibration is required. The prior art key sensors are respectively calibrated at the rest positions of the associated keys, only. However, there is a difference between the black keys and the white keys, and the individualities are still left after the calibration. For this reason, the calibration is imperfect, and the prior art key sensors do not accurately detect the current key positions.
On the other hand, the prior art key sensor disclosed in the aforementioned U.S. Patent is of the type having the flag held in contact with the associated key at all times. The key motion is transferred through the key action mechanism to the hammer, and the key action mechanism gives the unique key touch to the pianist at the escape of the jack from the hammer. The unique key touch is faint. The flag exerts the reaction against the depressed key, and the reaction damages the unique key touch. This is the first problem inherent in the prior art key sensor disclosed in the aforementioned U.S. Patent. The second problem is low accuracy. The prior art key sensor has position-to-potential converting characteristics, which are hardly represented by a linear line. The prior art key sensor does not accurately determine the current key position due to the non-linear converting characteristics.
Another problem inherent in both prior art key sensors is aged-based deterioration. Even if the manufacturer exactly calibrates the prior art key sensors, the actual position-to-voltage converting characteristics vary with time, and the key position becomes unreliable.
It is therefore an important object of the present invention to provide a position transducer system, which accurately recognizes the motion of a moving object.
It is also an important object of the present invention to provide a method for determining the position of a moving object which is used in a position transducer system.
It is also an important object of the present invention to provide a keyboard musical instrument, which accurately detects current positions of moving objects through the position transducer system.
In accordance with one aspect of the present invention, there is provided a position transducer system for determining a current position of a moving object movable along a trajectory, and the position transducer system comprises a non-contact type sensor monitoring the moving object and converting the current position of the moving object to a signal, a calibrator moving the movable object under standard conditions, connected to the non-contact type sensor and analyzing the signal for determining a relation between values of the signal and actual positions of the moving object and a corrector connected to the non-contact type sensor for receiving the signal and determining the current position of the moving object on the basis of the relation.
In accordance with another aspect of the present invention, there is provided a method for determining a current position of an object, comprising the steps of a) moving the object along a trajectory under standard conditions so as to obtain values of a signal representative of current positions on the trajectory, b) determining a relation between the values of the signal and the current positions and c) determining an actual position of the object moved under different conditions by comparing the value of the signal at the actual position with the values in the relation.
In accordance with yet another aspect of the present invention, there is provided a keyboard musical instrument comprising plural manipulators movable along respective trajectories between respective home positions and respective limit positions, a sound generating system generating sounds, and changing an attribute of the sounds depending upon the plural manipulators selectively depressed from the home positions, a position transducer system including plural non-contact type sensors respectively monitoring the plural manipulators and respectively converting the current positions of the associated manipulators to signals, a calibrator selectively moving the plural manipulators under standard conditions, connected to the non-contact type sensors and analyzing the signals for determining a relation between values of the associated signal and actual positions of each manipulator and a corrector connected to the non-contact type sensors for receiving the signals and determining the current positions of the plural manipulators on the basis of the relation and a controller connected between the corrector and the sound generating system, and responsive to the current positions determined by the corrector so as to instruct the sound generating system to change the attribute of the sounds.